Field of the Invention
The present invention mainly relates to oxynitride phosphors and nitride phosphors used for a light emitting apparatus, and methods of producing the same, and further to a light emitting apparatus having a light converter using the above phosphor.
Description of the Background Art
A light emitting apparatus having a combination of a semiconductor light emitting device and a phosphor attracts attention as a next-generation light emitting apparatus for which low power consumption, compact size, high intensity and high color gamut are expected, and research and development thereof is actively proceeded. As primary light that is emitted from a light emitting device, usually light from ultraviolet to blue range, more specifically from 380 nm to 480 nm is used. Also, light converters adapted to this application using various phosphors have been proposed.
Also in recent years, an attempt is made for the light emitting apparatus of this type to realize higher brightness by increasing not only luminous efficiency (brightness) but also input energy. When input energy is increased, it is necessary to effectively dissipate the heat of the entire light emitting apparatus including the light converter. For achieving this, development of the entire structure and material of light emitting apparatus has been proceeded, however, temperature rise in a light emitting device and light converter during operation is still inevitable.
Currently, as a light emitting apparatus exhibiting white light, mainly used is the combination of a light emitting device that emits blue light (peak wavelength: around 450 nm) and a trivalent cerium-activated (Y, Gd)3(Al, Ga)5O12 phosphor or a divalent europium-activated (Sr, Ba, Ca)2SiO4 phosphor that is excited by the above blue light and exhibits yellow light emission.
However, in the trivalent cerium-activated (Y, Gd)3(Al, Ga)5O12 phosphor, in particular, there is a technical problem that it is impossible to set input energy at high states because the luminance at 100° C. decreases to about 85%, compared to the luminance (brightness) of 100% at 25° C. Therefore, an oxynitride phosphor or a nitride phosphor having excellent temperature characteristics attracts attention and active development has been made.
However, in such an oxynitride phosphor or nitride phosphor, reflectance in the visible region is not sufficiently high despite the excellent characteristics, so that there is a technical problem that it absorbs light emitted from the phosphor itself or the light emitted from other phosphor. Therefore, in such an oxynitride phosphor or nitride phosphor, improvement in reflectance is urgently needed.
As to such an oxynitride phosphor or nitride phosphor, for example, Japanese Laid-Open Patent Publication No. 2002-363554 (Patent document 1) describes α-type SiAlON(SIALON). Specifically, Patent document 1 describes Ca-α-SiAlON phosphor activated with varying amounts of Eu2+ ion as a representative oxynitride phosphor or nitride phosphor. However, Patent document 1 lacks description about reflectance in the visible region of phosphor.
In Japanese Laid-Open Patent Publication No. 2006-089547 (Patent document 2), β-SiAlON: Eu which is a green phosphor and Ca-α-SiAlON: Eu which is an yellow phosphor are described. However, Patent document 2 also lacks description about the reflectance of phosphor in the visible region.
Furthermore, Japanese Laid-Open Patent Publication No. 2004-182780 (Patent document 3) describes a nitride phosphor that emits light of yellow to red regions represented by LxMyN((2/3)x+(4/3)y):R or LxMyOzN((2/3)x+(4/3)y-(2/3)z):R. However, even in Patent document 3, there is no description about the reflectance of phosphor in the visible region.
Japanese Laid-Open Patent Publication No. 10-228868 (Patent document 4) describes provision of a reflection-preventing film of silicon oxide or the like, on phosphor particles of europium-doped yttrium oxide, manganese-doped zinc silicate, europium-doped barium-magnesium-aluminum oxide or the like. However, Patent document 4 fails to describe reflectance of the phosphor itself.
Japanese Laid-Open Patent Publication No. 2004-155907 (Patent document 5) discloses an invention relating to a manganese-activated aluminate phosphor having green body color, which is excited by vacuum UV beam and emits green light having a peak wavelength of about 515 nm. A spectral reflectance in a vicinity of the peak wavelength or lower is improved to reduce absorption of light emitted from the phosphor and excitation light or vacuum UV light and thus increase light emission in luminance. However, the invention does not focus on a reflectance for a wavelength longer than the peak wavelength and does not consider absorption of light emitted from other phosphors, nor does it focus on visible light excitation.